[VM1973]

As far as I know most people play 2♦ over 2♣ as waiting, but some people use 2♦ as negative. A partner I used to play with said that you should use step responses, instead. Aces are 2 controls and kings are 1. Accordingly:
2♦ = 0-1 controls
2♥ = 2 controls (ace or 2 kings)
2♠ = 3 controls
2NT = 4 controls
etc.

What are the advantages and disadvantages of each treament?

[whereagles]

If you play that a 2♣ opener is made with REALLY big hands (i.e. just about game in hand), there might be a case for using control-showing responses. Otherwise you're better off with a response scheme that puts emphasis on what's more important, i.e. shape and strength.

The most usual method, in the latter case, is

- 2♦ = waiting, neutral with respect to strength. It can be followed later by 3♣, which is a 2nd negative, i.e. a hand that's likely to pass pard's rebid.
- 2/3x = natural, game forcing, decent suit

My favorite method is

- 2♦ = waiting, but game forcing
- 2♥ = immediate 2nd negative (opener now uses some relay or transfers)
- 2NT = heart suit, GF
- else = nat, GF

[mgoetze]

You can find a previous thread on 2♣ response structures on my systems index at http://bridge.mgoetze.net/bbf.html . It doesn't really contain a discussion of control responses because hardly any experts play them nowadays (though I know some intermediate-advanced players who do).

My personal advice to beginner/intermediate players is not to worry about this too much. Pick something you can remember even if it only comes up every other year and stick with it.